Paper-covered wood product and method of making same



March 20, 1951 R. J. BYERS ET AL PAPER-COVERED WOOD PRGDUCT AND METHODOF MAKING SAME Filed Dec. 22, 1947 EVENT [7P5 leap/v 1/ flaws Moss 5.(km/12m Patented Mar. 20, 1951 PAPER-COVERED WOOD PRODUCT AND' METHOD OFMAKING SAME Ralph J. Byers, Chicago, Ill., and Moss. B. Christian,Tallulah, La., assignors to Chicago Mill and Lumber Company, Chicago,Ill., a. corporation of Delaware Application December 22, 1947, SerialNo. 793,232.

Claims.

This. invention relates to the production of a dry, laminated paper andexpanded Wood veneer product formed from bonded-together wet,

swollen wood veneer and wet, expanded paper.

Specifically, the invention includes a papercovered expanded wood veneerproduct and a method of making the product from wet wood, wet paper, andwet glue, wherein the laminated assembly is dried only after the glue.bond is sufiiciently strong to prevent slippage between the paper andwood so that the paper will hold the wood in the expanded condition ofits wet state.

This application is a continuation in part of. our copending applicationentitled: Veneer and Method of Making Same, Serial No. 561,628, filedNovember 2, 1944, now Patent No. 2,442,115, granted May 25, 1948.

According to this invention, any species of wood, including woods thatwere heretofore unfit for use except as ,fuel, in its green, undried,and swollen state, is lathe-cut or peeled into a thin veneer sheet andis covered on both sides with sheets ofwet, expanded paper that havebeen coated with an alkalinized cold-setting, water-resistantprotein-type glue such as a sore bean glue or a locust bean glue. Theglue has a relatively high pH value (above '7) which reduces the surfacetension of the glue coating on the paper permitting water in the glue tobe rapidly absorbed into the paper. The water in the glue causes thepaper to expand and stretch and, in order to balance the expansion ofboth faces of the paper, the unglued face of the paper is moistened,preferably with a wax emulsion, although water alone can be used. Theglue-coated faces of the paper sheets are pressed against the veneerfaces under suflicient pressures to firmly contact the paper with thewood. The glue then sets rather rapidly because of absorption of some ofits water content by the paper, but the wood is not dewatered below 30%moisture content. A strong bond is formed so that slippage between thepaper and wood cannot occur. The assembly isthen subjected to anincreased pressure which will squeeze water out of the wood into thepaper to equalize or balance the moisture content of the wood and paper.This heavy pressure treatment will not affect the glue bond. After theheavy pressure treatment, the assembly is passed through a drying kilnwhere it is dried to a moisture content between 6 to 12 The termmoisture content as used herein and in the claims is based upon the ovendry weight of the wood and, when expressed in-terms 01' percentage,means the weight of the water present in the material divided by theoven dry weight (bone dry Weight) of the material multiplied by 100.Thus, it the moisture-laden wood sample weighed 10 lbs., and, when ovendried to a bone dry basis, it weighed 5 lbs., its moisture content,would be determined as follows:

Normally, wood beginsto shrink as its moisture content is reduced below30% and the shrinkage of wood from a green, wet state to a dry stateaverages about 10%. Further, normal shrinkage of wood brings about theformation of cracks and splits because the stronger bundled fiberportions will pull away from the weaker bundled portions as shrinkingprogresses. The present invention minimizes this shrinkage and thiscracking and splitting of wood, because the paper, which is bonded tothe Wood While it is Still in its wet, swollen condition, will hold theWood in it panded condition even after the moisture is driven therefrom.The product of the invention therefore includes a wood veneer core witht e Wood in an open mesh expanded condition free from splits or cracks.

It is, accordingly, an object of this invention to provide a laminatedpaper and wood product wherein the wood is substantially dry but held inan unshrunk condition by the paper and the non-slipping bond between thepaper and the wood.

Another obj ct of the invent on is t provide a paper-covered wood veneerproduct from green, undried wood, wet, expanded paper, and wet gluewithout permitting the wood to shrink substantially as the product isdried to a moisture content between 6 to 12%.

Another object of the invention is to provide a method of makingpaper-covered wood veneer from any species of green or wet woodincluding heretofore unusable woods, and paper which holds the wood inits expanded green state form even after the assembly is dried.

A specific object of the invention is to provide paper-covered woodveneer composed of tough kraft paper, wood veneer, and a water-resistantglue bond coacting with the paper to hold the wood in an expandedcondition.

A further object of the invention is to produce a paper-covered woodveneer product free from splits, cracks, loose knots, and other defectsnormally present in dry wood veneer.

Other and iilrther objects of the invention will become apparent tothose skilled in the art from the following description and from theannexed 3 sheet of drawings forming a part of this specification.

On the drawings:

Figure l is a somewhat diagrammatic side elevational view illustratingthe method of this invention for making the paper-covered wood productof this invention.

Figure 2 is a plan view of the product of this invention with successivelayers partially removed to show underlying layers.

Figure 3 is a cross-sectional view of the product taken along the lineIII-III of Figure 2.

Figure 4-. is a plan view of a veneer sheet, onehalf of which is coveredwith paper in accordance with this invention, and illustrating themanner in which the paper holds the wood veneer against shrinkage.

As shown on the drawings:

As illustrated in Figure l, a green wood log I is revolved against asuitable broad knife blade cutter i I of a veneer cutting lathe to forma thin green wood veneer sheet or ribbon H. The log [0 is in its green,undried condition and may even have live sap flowing therein. The loghas a moisture content above 30%, because most Woods begin to shrink atheir moisture content drops below 30 Usually the moisture content ofthe log will average about 130%. Woods such as gum, oak, cottonwood,sycamore, pine, and fir are examples of satisfactory species of wood toform the product of this invention. Woods that otherwise were unusableexcept for fueLzsuch as overcup white oak, are now rendered useful inveneer making. Heretofore such white oak woods checked and split to suchan extent when being dried that they were totally unfit for veneers andplywood panels.

The veneer sheet or ribbon I2 is quite thin and may have a thicknessvarying from .01 to 1% inch, with the thinner sheets in this range beingthe most economical. The veneer l2 has the grain running crosswise ortransversely of the sheet or ribbon. If necessary, pieces of veneer arestitched or stapled together to form a continuous sheet or ribbon i2.

Continuous sheets l3, (3 of unsized dry finish Fourdrinier kraft paperare unwound from rolls M and [5 respectively positioned above and belowthe veneer sheet E2. The sheet l3 from the roll l4 passes over a coatingroller I'G of a coating machine ll which applies an aqueous paraffin waxemulsion to the underface of the sheet. The sheet then travels under acoating roll l8 of a second coating machine [9 to receive, on its topface, a water solution of a soya bean glue. The sheet then passes arounda turning roll 2!] and has the adhesived face thereof deposited on topof the veneer [2 as the sheet passes under a roll 2|.

The sheet l3 from the roll [5 passes around a turning roll 22 and thenceover a coating roll 23 of a coating machine 24 which deposits an aqueouswax emulsion on one face of the sheet. The sheet then travels aroundguide rolls 25 to the, coating roll 26 of a second coating machine 21which adhesive-coats the opposite face of the sheet with the soya beanglue. The adhesived sheet then passes around a turning roll 28 and ispressed against the underface of the veneer ribbon [2 by means of a roll29.

The Fourdrinier kraft paper is tough, waterabsorptive, and of a typecommonly used for liner board. The fibers of the paper run lengthwise ofthe sheet and thus the fibers of the wood and paper are at substantiallyright angles to each 4 other. The kraft paper weighs from 26 to lbs. perthousand square feet, and a 42-lb. paper is a preferred average.

The wax emulsion deposited on the sheet by the coating machines I1 and24 is composed of paraffin wax and water in suitable emulifiedcondition. The wax is used to impart a smooth finish to the outer faceof the paper but it is not essential to this invention. The water of theemulsion moistens the outer faces of the sheet l3 so that the Water fromthe glue, which is applied to the inner faces of the sheets, will notunevenly expand the paper causing it to curl and buckle. From 2 to 10%of water, based on the Weight of the paper, is added to the outer facesof the sheets by the coating machines I! and 24 with 5% forming apreferred average.

The soya bean glue applied to the inner faces of the sheets by thecoating machines I9 and 21 is composed of soya bean flour of arelatively fine mesh, water, and caustic soda in sufficient amounts toform a soya bean glue. From 30 to of water, based on the weight of thepaper, is added by the glue to the inner faces of the paper sheet, withabout 80% forming a desired average. The caustic soda gives the glue ahigh pH value, reducing its surface tension and speeding up absorptionof water from the glue film into the paper. This water absorption, inturn, speeds up setting of the glue.

The paper sheets I3, wet on both faces by water in the wax emulsion andwater in the glue, will expand and stretch, and a sufficient amount oftime elapse from the water application to the point of deposition of theadhesive-coated faces of the paper on the veneer ribbon l2 so that thepaper can expand.

The total moisture content in the paper preferably balances the totalmoisture content of the wood and the glue preferably applies moremoisture to the inner face of the paper than the wax emulsion applies tothe outer face of the paper.

The paper covered veneer ribbon passes from the first pair of squeezerolls, composed of rolls 2| and 29, between a series of small diameterpress rolls 30. These press rolls are not driven. From the smalldiameter rolls 30, the assembly passes between larger diameter drivenpress rolls 3!. The press rolls 3liapply a pressure of about 7 lbs.

per square inch on the assembly while the larger diameter driven pressrolls 3! apply. pressures within the range of '75 to lbs. per squareinch on the assembly. These press rolls 3!] and 31 firmly press thepaper against the Wood and insure good bonding contact between the paperand wood. The rolls 3!! and 3| are unheated and suf-. ficient timeelapses during the passage of the assembly through these rolls so thatthe soya bean glue can cold set to a point where a bond is formed thatwill prevent relative slippage between the paper and wood. The cold bondis actually stronger than the paper itself, so that slippage, cannotpossibly occur. 7

The heavy pressure rolls 3! are effective tosqueeze water out of thewood and equalize the- Water contents of the wood and paper. Forexample, the paper may lose moisture by evapora-- tion as it passes fromthe coating machine through the pressure rolls 30, and the high pres-"sure rolls 3| will drive moisture out of the wood into the paper tocompensate for this loss of. moisture by evaporation.

bon is cut by a cutter 32 into panels 33 of the desired length; Thesepanels are fed by a conveyor '34 to a drying kiln '35 where they passbetween pressing rolls 36 so that the laminated assembly is hot pressedafter the cold pressing operation. The drying kiln has an inlettemperature of about 250 F. and an outlet tem-. perature of about 375 F..The panels 33 are dried to a moisture content between 6 to 12%, andpreferably to a moisture content of 8%. The finished product 31 issuingfrom the drying kiln '35 has substantially the same dimensions as theoriginal wet material from which it was formed. Shrinkages averaging1.5% or less are encountered, and these shrinkages are represented byuniform shrinking of the expanded wood and expanded paper so thatpuckering and wrinkling of the paper does not occur. This shrinkage isless than of the normal shrinkage of wood from its green, wet stage toits dry state.

' As shown in Figures 2 and 3, the product 3'! is composed of anintermediate sheet or .core 38 of wood veneer which is dry, but still inthe expanded swollen condition of its green state. Thus the veneer isfull of pores 38a that were formerly filled with water, but is free fromcracks, splits, or checks normally present in dried wood. Any knots,such as 38b, are tight in the body of the wood, because the wood has notshrunk away from the knots. Both faces of the wood core 38 are coveredwith paper sheets 39. These paper sheets 39 have smooth, glazed outerfaces 390. containing wax from the emulsion. Glue bonds 4B firmly unitethe inner faces of the sheets 38 to the wood core. Some of the gluepenetrates into the core and paper, but does not bleed completelythrough the paper.

As illustrated in Figure 4, the paper faces 39 hold the wood coreagainst shrinkage. Thus the half portion of the core which is uncoveredby the paper is in a shrunken, dried condition, full of cracks andsplits 380, while the papercovered portion of the veneer is uniformlyporous. The grain of the paper extends along the length of the ribbonand is at right angles to the grain of the wood core so that thecross-banding effect of plywood is obtained.

The paper-covered wood veneer of this invention has a tensile strengthof almost three times the tensile strength of the veneer wood from whichit is formed. It has a puncture resistance of almost four times theresistance of the uncovered veneer wood. The product is nailable andsawable in the same manner as plywood or lumber, and is especiallyuseful in the production of boxes and crates. The soya bean glue whendried forms a bond which is water resistant and the product willeffectively resist weather conditions. The uniform moisture content of 6to 12% in the finished product prevents buckling and warpingirrespective of atmospheric humidity changes.

From the above descriptions it should be understood that this inventionprovides a papercovered wood veneer according to a continuous methodfrom wet green wood, wet glue, and wet paper, which prevents shrinkageof the wood so that the finished dry product maintains substantially thesame dimensions as the green wood from which it is formed.

It will, of course, be understood-that various details of the productand method may be varied through a wide range without departing from theprinciples of this invention and it is, therefore, not the purpose tolimit the patent granted hereonothe'rwise than necessitated by the scopeof the appended claims.

- We claim as our invention:

l. A composite board formed from green woo having a moisture contentabove 30%, flexible absorbent paper, and a water-resistant glue, whichcomprises a dry wood veneer sheet containing from 6 to 12% moisture butremaining in the swollen green wood expanded condition, a sheet ofabsorbent paper united to said veneer sheet and containing moistureabsorbed from the wood, said paper having a moisture content of about 6to 12%, and an alkalinized cold set waterresistant protein glue bondfixedly uniting the paper and wood in non-slipping relation and causingthe paper to hold the wood in the expanded form.

2. A pliable veneer panel which comprises a sheet of wood veneercontaining from 6 to 12% moisture but having the cells thereof in theswollen expanded form of green wood, a sheet of unsized tough kraftpaper covering each face of the veneer, an alkalinized soya bean gluefixedly uniting the paper sheets with the veneer in non-slippingrelation and causing the paper to hold the wood in the expandedcondition, said soya bean glue having a pH value above 7 and effectiveto reduce the surface tension of the glue coating on the paper tofacilitate absorption of the glue into the paper, and a wax surface ontheouter faces of the paper sheets providing a smooth finish to thesurfaces of the panel.

3. The method of making a laminated board which comprises providing asheet of Wet wood veneer containing more than 30% moisture, applyingmoisture to one face of each of two sheets of paper, applying to theopposite face of each of said sheets of paper an aqueous alkaline gluesolution capable of forming a non-slipping bond between the paper andwood prior to removal of the moisture from the wood, allowing the paperto expand, pressing the glued face of one sheet of the expanded paperagainst one face of the wood veneer, pressing the glued face of theother sheet of the expanded paper against the opposite face of the woodveneer and thereby firmly contacting the glue with both faces of thewood, setting the glue before the wood begins to shrink to form anon-slipping bond between the paper and the unshrunk wood, subjectingthe assembly to increased pressure to squeeze water from the wood intothe paper for balancing the moisture conditions of the wood and thepaper, and drying the laminated assembly to a moisttu e content between6 to 12% whereby the non-slipping bond between the paper and wood willcause the paper to hold the wood in its open mesh expanded swollencondition even after the moisture content of the wood is reduced belowthe point where the wood normally begins to shrink.

4. The method of making paper-covered wood veneer from green wood veneercontaining more than 30% moisture which comprises moistening one face ofeach of two sheets of tough paper with water, applying to the other faceof each of said two sheets of paper a water solution of a soya bean gluecapable of forming a non-slipping bond between the paper and green woodprior to removal of the moisture from the green wood, allowing themoistened sheets to expand, depositing the glued face of one expandedsheet on one face of the green wood veneer, depositing the glued face ofthe other expanded sheet'on the opposite face of said green wood veneer,pressing 76 both sheets of the paper against the green WOOd veneer tofirmly contact the glue with both the paper and the wood, setting theglue before the moisture content of the wood is reduced below 30% andthereby uniting the wood and paper in non-slipping relation, furtherpressing the assembly to squeeze water from the wood into the paper forbalancing the moisture conditions of the wood and paper, and drying theassembly to a moisture content between 6 to 12% and thereby furthersetting the glue, whereby the paper will hold the wood in its expandedswollen green wood form.

5. The method of making paper-coveredwood veneer from a ribbon of greenwood veneer containing more than 30% moisture which comprises coatingone face of each of two sheets of tough kraft paper with an aqueous waxemulsion, coating the opposite face of each of said two sheets of paperwith an aqueous soya bean glue capable of forming a non-slipping bondbetween the paper and the ribbon of green wood prior to removal of themoisture from the wood, allowing the sheets of paper to expand due tothe increased moisture content added thereto by the Wax emulsion and theglue, depositing the glue-coated face of one of said expanded papersheets on a face of the green Wood veneer, depositing the gluecoatedface of the other of said expanded sheets of paper on the opposite faceof said green wood veneer, pressing the assembly together to firmlyunite the paper and wood before the wood begins to shrink, setting theglue to form a non-slipping bond between the paper and the wood whilethe woodstill has a moisture content over 30%, subjecting the assemblyto increased pressures for squeezing moisture from the wood into thepaper, and thereafter drying the assembly to a moisture content between6 to 12% while said paper holds the wood in its expanded green woodcondition.

RALPH J. BYERS. MOSS B. CHRISTIAN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,125,973 Davidson Jan. 26, 19151,369,743 Hood et a1. Feb. 22, 1921 1,714,858 Elmendorf May 28, 19291,714,859 Elmendorf May 28, 1929 1,997,344 Randall et al. Apr. 9, 19351,999,253 Norris Apr. 30, 1935 2,095,389 Kondolf Oct. 12, 1937 2,271,620Brier et al Feb. 3,1942 2,325,584 Barnhart Aug. 3, 1943 2,372,617 Trew LMar. 27, 1945 2,425,660 Ware et al. Aug. 12, 1947 2,442,115 Byers et alMay 25, 1948

